Article 4, Section 2, Clause 3 of the Constitution places the subject of slavery within the purview of the States, not the federal government.
This concept is reiterated in the historical records.
{Sorry for the need to cut & paste - the Library of Congress disables a link]
Mr. HUGH L. WHITE. When the Constitution was framed, the great and leading interests of the whole country were considered, and, in the spirit of liberality and compromise, were adjusted and settled. They were settled upon principles that ought to remain undisturbed so long as the Constitution lasts, which I hope will be forever; for although liberty may be preferable to the Union, yet I think the Union is indispensable to the security of liberty. At the formation of the Constitution, slavery existed in many of the states; it was one of the prominent interests that was then settled. It, in all its domestic bearings, was left exclusively to the respective states to do with as they might think best, without any interference on the part of the federal government.
http://memory.loc.gov/cgi-bin/ampage?collId=lled&fileName=004/lled004.db&recNum=607&itemLink=D?hlaw:1:./temp/~ammem_uMGu::%230040608&linkText=1
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Journal of the Senate of the United States of America, 1789-1873 / SATURDAY, March 2, 1861.
Article 6. No future amendment of the Constitution shall affect the five preceding articles, nor the third paragraph of the second section of the first article of the Constitution, nor the third paragraph of the second section of the fourth article of said Constitution, and no amendment shall be made to the Constitution which will authorize or give to Congress any power to abolish or interfere with slavery in any of the States by whose laws it is or may be allowed or permitted.
http://memory.loc.gov/cgi-bin/ampage?collId=llsj&fileName=052/llsj052.db&recNum=378&itemLink=r?ammem/hlaw:@field(DOCID+@lit(sj05267))%230520379&linkText=1
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So, no - the superficial cause was slavery.
The underlying cause was the federal government (along with no too few of the other States) were abridging the Constitution, and eroding the oh-so-carefully drawn lines between federal and each sovereign State's authority.
MamaTexan,
I agree with you the usurpation of power by the federal government was definitely part of the reason for secession.
Another HUGE issue was that Southerners well understood after the Tariff of Abominations and the Nullification Crisis the effect that very high protective tariffs would have on their economy and they well understood that the Northern states - via their congressional majority due to their larger population - were voting themselves a hugely disproportionate share of federal largesse raised from those high protective tariffs paid by Southern Exporter/Importers be it for mining and railroad subsidies, fishing subsidies, infrastructure projects, etc etc. They also understood that in addition, a high protective tariff on manufactured goods would have the effect of raising prices - thus once again benefiting the Northern states which did the vast majority of the manufacturing.
The Southern economy was geared toward the export of cash crops. The economic legislation that would be beneficial to them was the exact opposite of what would most benefit the Northern states which were industrializing at the time.
As always, people fight about money.
The economy of the South was dependent on staple agriculture mostly of the agribusiness plantation form. The Republicans who were just Hamilton's descendents and mostly northern Whigs knew their crony capitalist model which was their true core reason to exist would never attract enough votes to defeat the Democrats. So the GOP spent a decade screaming about slavery to troll for enough voters in the north to give them the edge. Lincoln and Seward could care the less about slavery as long as it stayed in the South and Southerners paid most of the cost of the tariffs on manufactured items. With that dough they could pay off the speculators and bankers and railway interests that were the powerbase of the party.
Unfortunately people in the South believed windbags like Seward and after the events surrounding John Brown believed they were facing an existential threat from the north of the most basic kind. Lincoln never figured that out as did many northerners and were shocked and then outraged when they realized the South was serious about forming its own country and breaking the rice bowls of many northern capitalists.
This I think is the real basis for the secession crisis and the war that followed. It is much to grubby to justify the hideous destruction of the war and the hundreds of thousands of casualties so the ‘glory, glory, hallelujah, version became the default.
If that is true then why did the Confederate states adopt a Constitution where the federal government mandated slavery would be allowed in all states and territories, mandated that no state could be a non-slave state, and mandated that the states could not end slavery by constitutional amendment? Isn't that an even larger abridgement of the state's sovereignty?